There are two methods to install skins, if using Curse.com the best and simplest is to use the Curse client (V5). It will install the skin in the correct location. Just select your skin from the Curse mod menu and select install, its that easy. The second way is the manual method and the one used if downloading directly from this website.
The detailed description on how to manually installation and change a custom skins has moved to Grandpa’s Custom Skin Installation